Examples of applications of the invention are found in hydraulically operated implement systems for earth moving equipment, in hydraulic systems for hydraulically operated dump truck mounted dumping mechanisms, packing mechanisms in refuse collection equipment and in auxiliary hydraulic systems for power steering units, brake systems and the like.
The invention provides a solution to the problems of noise and power loss in equipment of the kind described above. In such equipment it is customary and desirable practice that the hydraulic pumps for operating auxiliary equipment be driven by the same engine which provides the motive power for the vehicle. In many of the applications for such equipment, ample power is available for the hydraulic pump, because the requirements for use of the pump usually don't coincide with the requirements on the engine for driving the vehicle from place to place.
At typical vehicle running speeds however, unless means are provided for disengaging the pump from the engine, considerable engine horsepower is used by the pump in circulating hydraulic fluid through the hydraulic system. This wastes power and hence fuel and is a significant source of hydraulic noise since the noise level in hydraulic systems increases directly with pump speed.
As a means for solving the noise problem, it is known to use a large pump having sufficient capacity to operate the auxiliary equipment when the pump is operated at or near the idling speed of the vehicle engine. A clutch is provided so that when the vehicle is in motion, the operator can disengage the pump. According to one known solution employing a large capacity pump, a centrifugal clutch is used to disengage the pump at high running speeds where noise becomes objectionable. In addition, it is known to use multiple pumps and to divert part of the output of the pumps back to the fluid reservoir in the event of particular upper flow rates or pressure values as a means of minimizing noise.